1. Field of the Invention
This invention relates to digital data signal transmission, and in particular, it relates to a signal extender system for transmitting digital data signals with a single cable.
2. Description of the Related Art
In recent years, with the constant evolution of electronic technology, multimedia audio-visual (A/V) technology has developed very rapidly. One example is the High Definition Multimedia Interface (HDMI) used for integrated A/V signal transmission. Since a single HDMI cable can be used for transmitting non-compressed audio signals and high resolution video signals, there is no need to convert analog into digital (A/D) signals or digital into an analog signal (D/A), so the A/V signals can be transmitted without distortion.
Referring to FIG. 1a, there is shown at 100 a typical conventional arrangement for transmitting A/V signals between a signal source device 110 and a signal sink (target) device 120. The signal source 110 has an HDMI output terminal 112, and the signal sink 120 has an HDMI input terminal 122. For short local distance transmission, an HDMI cable 132 may be used to directly couple HDMI terminals 112 and 122 for transmitting A/V signals from the source 110 to sink 120. The major limitation of this arrangement is the short distance between the source 110 and sink 120, as HDMI cables are usually very bulky and expansive and only made in a length of a few feet.
Referring to FIG. 1b, there is shown at 102 another conventional arrangement for transmitting audio-video (A/V) signals such as digital visual interface (DVI) or HDMI, utilizing two Category 5 (CAT-5) cables for longer distance transmission between the source 110 and sink 120. A signal extender 140 is provided between the source 110 and sink 120. The extender 140 includes a transmitting (TX) module 150 and a receiving (RX) module 160. The TX module 150 has an A/V input terminal 152 and two CAT-5 output terminals 154 and 156. The RX module 160 has an A/V output terminal 162 and two CAT-5 input terminals 164 and 166.
An A/V cable 132 is coupled between A/V terminals 112 and 152 to connect the source 110 and the TX module 150, and another A/V cable 132′ is coupled between A/V terminals 162 and 122 to connect the RX module 160 and sink 120. Two CAT-5 twisted pair cables 174 and 176 are used to connect TX module 150 and RX module 160, wherein CAT-5 cable 174 is coupled between CAT-5 terminals 154 and 164, and CAT-5 cable 176 is coupled between CAT-5 terminals 156 and 166.
However, there are still major limitations with this arrangement. First, the transmission distance is still relatively short. For example, for transmitting 1,080P digital image differential signal, since the video image has a high resolution of 1,920×1,080 (with 1,080 horizontal lines) which requires a relatively larger bandwidth of about 1.86 Gbps, CAT-5 cables can only reliably transmit 1,650 MHz differential signal for about 120 ft. When an HDMI source and an HDMI sink are located further away, the signal extender system for transmitting A/V signals from the source to the sink usually needs to incorporate one or more repeaters in its design.
Second, a CAT-5 twisted pair cable has only four (4) pairs of differential transmission lines, which are merely enough for transmitting differential data signals. However, other control signals provided by the A/V source 110, including the inter-integrated circuit (I2C) signal, the Consumer Electronic Control (CEC) signal, the Hot Plug Detect (HPD) signal and the power supply signal VDD, must also be transmitted to the sink 120. In addition, the I2C is a bi-directional signal not suitable to be carried by the one-way differential data signal. As a result, two CAT-5 cables 174 and 176 must be used so that both differential data signal and other control signals (e.g., I2C/CEC/HPD/VDD) can be transmitted between the TX module 150 and RX module 160.
Referring to FIG. 1c, the data signals transmitted from the source 110 to the TX module 150 by the A/V cable 132 includes digital A/V differential data signals D0±, D1±, D2±, differential clock signal CLK±, and other control signals such as I2C, HPD, VDD and CEC signals. The two CAT-5 cables 174 and 176 coupled between the TX module 250 and the RX module 260 each has four pairs of differential transmission lines L1, L2, L3 and L4. The four pairs of differential transmission lines L1, L2, L3 and L4 of the first CAT-5 cable 174 may be used for transmitting differential data signals D0±, D1±, D2± and differential clock signal CLK±. The four pairs of differential transmission lines L1, L2, L3 and L4 of the second CAT-5 cable 176 are used for transmitting the other control signals I2C/HPD/VDD/CEC. Therefore two CAT-5 cables are needed conventionally.
There is a need to have an improved signal extender system that can use a single signal cable for carrying digital multimedia signals from a source device and transmit the digital multimedia signals in longer distance.